For the past several years our laboratory has been engaged in outlining the connections of the cerebral cortex in rhesus monkey, in association with the investigation of its functional implications. We wish to investigate further the connections of the cerebral cortex by widening our technical base by employing recently developed procedures. We are planning to use autoradiographic and protein transport histochemical methods. These new techniques in combination with light and electron microscopic procedures already in use will greatly enhance our further investigation dealing with the organization of cortico-cortical connections. Currently we are addressing ourselves to the following problems. (1) the nature of sensory association input to the prefrontal cortex, with special emphasis on sensory association areas receiving input from more than one modality; (2) the nature of sensory association input to the inferior parietal lobule and temporal association cortex (superior temporal sulcus); (3) the nature of sensory association input to the parahippocampal areas including the fusiform, perirhinal and entorhinal areas; (4) the efferent connections of the cingulate gyrus including a Golgi stain analysis of the retrosplenial subdivision of this area; (5) the organization of the afferent input to the auditory cortex including an electron microscopic analysis of the laminar organization of the connections; (6) functional significance of cortico-cortical multi-modal association input to the periarcuate region as well as parieto-temporal association areas.